I wasn't sure if this was the right forum to ask this question on, so moderators please feel free to move the thread to a more appropriate forum.

I ended up picking up a pretty large ponderosa this weekend, which I believe was supplied by Oregon Bonsai (or some other collectors in Oregon). I would post pictures of my new tree, but it's been raining every day for the past month so it's a bit difficult to pull the camera out.

It's in a nursery container at the moment, and is in what looks like pure pumice with particles in the 1/4"+ size. I may repot it this spring given that it's been in this container for what sounds like at least 3 years to remove some of the native soil and refresh the pumice mixture.

I currently have my ponderosas (which are on the smaller side) in a mix that is primarily composed of smaller particles of pumice (from Dry Stall), lava and grit, but I'm thinking of using the larger size because of the size of the tree and because the tree seems very happy in that medium. It sounds like the guys in Oregon swear by it, but I haven't seen pumice of this size on the East Coast - does anyone have any sources for pumice this size?

Only place I know of that would ship it to you is Bonsai by Fields, in Indianapolis. I get my lava from Mark Fields or from Scott Yelich (Eagle Creek Bonsai,) also in Indy. I don't think Scott ships it, tho. (I don't worry about shipping since I coordinate my purchases with visits to family in Indy. )

North Star Bonsai, in York, PA, also shipped lava, but their website has been pretty much abandoned for several months. Tom may still have his store; I can give you a phone number if you want. Just send me a PM if you do.

Just to be clear, though - there is a difference between lava and pumice, right? I've got a tree (collected spruce) that is in pure pumice and was told that pumice is particularly good for developing roots on collected trees. Judging from what I see at the bottom of the pot, that seems to be true...but have people found that regular lava rock performs similarly? I can get lava locally, but not pumice.

Just to be clear, though - there is a difference between lava and pumice, right? ...

Chris

Here's another occasion where the flexibility of language can turn into ambiguity! Technically, "lava" is molten rock once it comes out of the earth. (When it's still underground, it's "magma.") As lava cools, it hardens into many different kinds of rock: basalt, granite, obsidian, pumice, and I'm sure many others. They're all called "igneous" rocks, because they result from the cooling of lava.

These cooled-lava products -- "igneous rocks" -- have different densities, different properties in general, depending on the speed with which they cool and the various minerals and gases in the lava. That's how we get everything from basalt, which is quite dense and heavy, to pumice, which floats!

OK, enough layman's-level geology. In the bonsai world, we use "pumice" as geologists do: for a very porous, very light volcanic product, that usually floats. We tend to use "lava" for a similar volcanic rock that, while still porous and fairly lightweight, isn't as light or as porous as pumice. (I don't know what a geologist would call what we call bonsaiists call "lava.")

I hope this helps a bit! And if there are any trained geologists out there who spot any mistakes in what I said, I'm open to correction.

Some folks say that pumice (like Hyuga or that from the West Coast) and Volcanic (scoria) are interchangeable. I haven't tried to replace one with the other, I do know that the 1/4" Volcanic has lots of debris and dust that has to be removed. We use a mix that has both, I also use a mix that Kiryu in it, so I think the key is to have a good uniform mix that provides adequate drainage and aeration yet holds some moisture to keep the roots happy (humid but not soggy....). JOhn

Thanks very much everyone. The Wee Tree pumice looks like it might work, though it appears to still be a bit smaller than what my ponderosa currently is potted in - but maybe my sense of scale is off.

Just out of curiosity, where are people finding larger particle soil components for their larger trees? I've seen larger sized japanese soils (akadama and kanuma), but aside from possibly larger sized lava, I haven't seen too many domestically sourced options. Turface, haydite, grit, etc. seem to be on the smaller side.

... I think the key is to have a good uniform mix that provides adequate drainage and aeration yet holds some moisture to keep the roots happy (humid but not soggy....). JOhn

I think you nailed it, John. Tho I still wonder if organic materials don't have a place, because of their cation-exchange capacity. Any thoughts on that, anyone?

Mike, I've run into the same thing when it comes to particle size. I spent a couple of hours yesterday sifting a 50-lb bag of Turface; particles over 2 mm I use in my mix, the rest -- and it was about 40% of the total -- at least can be used as a drying agent in the dogs' run!

I think we see this issue because we're taking products made for other purposes, and adapting them to bonsai use.

Thanks for the explanation...I did know that and was wondering if there is a clearly defined "breakpoint" where the lava product goes from being called "lava rock" (or whatever) to "pumice", and whether that is important in terms of its use in bonsai soil. I have "pumice" in 2 forms - the first, fairly large particle size (1/4 inch and larger) is from a collected spruce that I picked up at Natures Way Nursery this spring (tree is originally from Oregon, don't know who collected it). The second was a batch of pumice sent to me by a member on another forum, and is much smaller - more similar to the particle size of turface. I just tested both in water and found that most of the smaller pumice (batch 2) sinks. For the larger particles from the spruce, about 1/3 to 1/2 float, and the rest sink.

In contrast, red lava rock - which I was able to obtain locally - is definitely denser and all of that sinks in water.

The reason I'm interested in this topic - the spruce will most likely be repotted in the spring, and I will probably want to put it back into pumice or the equivalent for a couple more years. Since I haven't been able to find the larger size pumice locally, I'm wondering if what I have can be "extended" with the lava rock, which I can get in the same size...or if I should look for larger particle size "pumice", like what WeeTree appears to have available.

Chris

P.S. A good use I've found for the sifted turface "fines" is adding them to my growing beds to improve the soil structure.

I have several ponderosas from Oregon Bonsai that came in the same pumice you have talked about. I have not found any around here, so when repotting I've combined the old pumice with some new lava rock and they are doing OK.

I'm no geologist, but do have a science background, and I can't see how pumice would have any special properties that lava would not also have. Maybe one holds on to water a little better than the other? But you'd have to do side-by side comparisons to know for sure. I doubt it would make a large difference regardless.

OK since writing that paragraph I did a little research (gotta love google.) I think what we call lava rock is what geologists call "scoria." Essentially, scoria is porous volcanic rock with a density greater than 1 (sinks in water) while pumice is porous volcanic rock with a desity less than 1 (floats in water.) Scoria may have higher concentrations of metals such as iron, but that's the only difference I've been able to find so far.

So I would say it's probably not necessary for you to pay to ship pumice across the country if you can find lava locally.

Pumice is formed from Rhyolite lava as it expands and becomes frothy. Scoria forms when the same process occurs with Basalt lava. Thus there chemical compositions are a little different. Pumice is considered a felsic rock, while scoria is a mafic rock. See my links below for the full definitions, but essentially, pumice has more silica while scoria has more metals like iron. They also have different proportions of feldspars.

So what does that mean horticulturally? I could only find one decent link that talked about horticulture, and it didn't have alot to say about the differences. Sounds like a good topic for a school science fair project.

So there may be some differences. Enough to justify the shipping cost across the country? Probably not.